It is contemporary practice to combust fuels together with fuel additives in cylinders of internal combustion engines, wherein the fuel additives assist to protect the engines from oxidative corrosion, as well as providing a degree of lubrication and cetane control In certain engines, the fuel includes an additive, such that the fuel and additive are injected through a same nozzle of a given cylinder; conversely, in other engines, an additive is injected separately to a hydrocarbon fuel into cylinders, by using multiple nozzles per cylinder.
Polyethylene glycol dinitrate (PEGDN) is a known additive for use with hydrocarbon fuels. Moreover, it is known practice to manufacture PEG nitrate in a two-step chemical process as provided in Table 1.
TABLE 1Known PEGDN manufacturing processStepReaction1nC2H4O + H2O → HO—(CH2CH2—O)nH2ROH + HNO3 → R—O—N═O═O
In Table 1, “R” represents a molecular grouping including ethylene glycol.
In a known publication “Organic Chemistry of Explosives (2007)” by P. Agrawal and R D. Hodgson, there is described a mixed acid generated from sulphuric and nitric acids, which still remains a most important reagent for the industrial production of nitrate esters:

Generally, nitrations with mixed acid and nitric acid are exothermic. Therefore, on a large scale, there is always a potential problem of thermal runaway and an associated risk of explosion. Consequently, on an industrial scale, the mixed acid nitration of polyols requires strict control, including:    (i) remote handling;    (ii) elaborate reactors; and    (iii) blast-proof buildings.
Further, conventional nitration usually follows a batch or a semi-batch approach, where the mixing of reactants and the reaction itself are carried out very slowly. A continuous process has also been claimed by Corning Incorporated USA, using their Advanced Flow Reactor. However, specifically for the production of PEGDN, some of the most important concerns, which do not allow for an easy scale-up include: (i) an inadequate heat transfer area, (ii) an inhomogeneous system, mainly due to immiscible substrates and inefficient mixing, leading to mass transfer limitations, (iii) batch to batch variation in the degree of conversion, yield and selectivity, (iv) prolonged reaction times, (v) reactions at very low temperatures to reduce the rate of heat generation, (vi) the use of excess nitrating agent, mainly the spent acid, which occupies significant volume, has to be neutralized thereby needing large quantity of water, and generates inorganic salts.
Moreover, product separation may be a frequent problem associated with the mixed acid nitration of polyols. There arises a mixed acid residue from the method, and associated aqueous washings often contain considerable amounts of dissolved nitrate ester, presenting both a safety and a waste problem; ethylene glycol dinitrate is soluble in water to the extent of 0.5 g per 100 ml.
Therefore, there is a need for improved apparatus and method of producing fuel additives, for example based on ethylene glycol nitrates, for example PEG, which address aforementioned problems more effectively.